The present invention relates to hydrophone calibrators in general and more particularly pertains to a calibrator for measuring the directivity pattern and sensitivity of a line-hydrophone array.
The utility of a hydrophone array is dependent on the accuracy with which it has been calibrated. Accurate determination of the directivity pattern and complex sensitivity of an array are required for the sophisticated demands of modern marine technology. The directivity pattern of an array is the dependence of the array output signal amplitude on the incident angle of an acoustic plane wave incident on the array. The complex sensitivity is the dependence of the amplitude and phase of the array output signal on the amplitude and phase of the incident acoustic plane wave at the center of the array. The complex sensitivity must be known as a function of frequency.
Heretofore, arrays have been calibrated in natural bodies of water or in calibration chambers. As the length of hydrophone arrays has increased it has become increasingly difficult to obtain free field conditions, necessary for directivity measurements in natural bodies of water. The long arrays are also impossible to fit in prior art calibration tanks without coiling or winding the array on an acoustically transparent drum. However, when the arrays are coiled or wound directivity measurements are precluded.